Production of nuclear fuel pins used in fast flux breeder reactors involves placing plutonium and uranium oxide fuel pellets within a relatively long tubular fuel pin casing. Plutonium oxides are highly toxic to humans therefore requiring that the fuel pins be loaded within a fully contained production facility. Recently designed nuclear fuel pin assembly systems are preferably completely automated to substantially eliminate the need for human interaction in the assembly process.
An automated nuclear fuel pin assembly system has been developed which incorporates a first section in which the fuel pin casings are loaded with the nuclear fuel pellets. In this first section a nitrogen atmosphere is maintained. The system also uses a second section which must be separate from the first section because it uses a 98% pure helium atmosphere. Helium is used to increase heat transfer from the nuclear fuel pellets to the fuel pin casing during operation of the reactor.
Loaded fuel pins must be transferred from the first section to the second section but this creates problems of leakage of nitrogen into the second section which must be maintained as nearly pure helium. Leakage occurs not only because of direct flow of gases between the sections but also because of nitrogen gas which is diffused into the pellets. Complete removal of nitrogen gas diffused within the fuel pellets takes approximately two to four hours under a vacuum of 10.sup.-5 torr.
The intended production rate of such a plant is one fuel pin every two minutes. Since removal of the nitrogen gas requires approximately four hours it is necessary for an evacuate and backfill subsystem to be used so that a large number of fuel pins can be simultaneously evacuated to remove nitrogen. The evacuated fuel pins are then backfilled with helium and sent on to the second section. In the second section the fuel pins are sealed by pulsed magnetically welding an end cap into the open end of the fuel pin casing.
It is an object of the invention to provide a new and useful apparatus for and method of automatically evacuating a multiplicity of hollow articles and purging or backfilling the same with a desired gas.
It is another object of the invention to provide an evacuate and backfill apparatus which is fully automated and which receives and emits fuel pins in an endwise direction.
It is still another object of the invention to provide an evacuate and backfill apparatus which can maintain vacuum pressures having a very low absolute pressure level.
It is yet another object of the invention to provide an evacuate and backfill apparatus which delicately handles elongated pins while they are being processed therein.
It is a further object of the invention to provide an evacuate and backfill apparatus which receives and emits elongated pins in a singular fashion for subsequent treatment by related automated processing equipment.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.